1. Field of the Invention
The present invention relates to a backlight of a liquid crystal display device, and in particular to a spread illuminating apparatus that is suitable as a backlight for a liquid crystal display device used in a naked eye 3D display system.
2. Description of the Related Art
Recently, a naked eye 3D display system in which a viewer can visually recognize a stereoscopic (3D) image without using a specialized tool such as glasses has been attracting attention. Conventionally, in such a naked eye 3D display system, a technology has been proposed in which a left-eye image and a right-eye image displayed on a liquid crystal display device are respectively supplied to only the left eye and only the right eye by light distribution control of illumination light from a backlight, and thereby the naked eye 3D image is realized (for example, refer to Japanese Patent Application National Publication No. 2010-541020).
As shown in FIG. 7, such a display device 110 includes a liquid crystal display panel 120, a backlight 130 that supplies light to the liquid crystal display panel 120, and a two-sided prism film 140 that is disposed between the liquid crystal display panel 120 and the backlight 130. The backlight 130 includes a light guide plate 125, a right-eye image solid-state light source 132 disposed on a first light input surface 131 of the light guide plate 125, and a left-eye image solid-state light source 134 disposed on a second light input surface 133. On an underside surface 136 of the light guide plate 125, a linear prism is formed across the entire surface as an optical path conversion unit.
In the two-sided prism film 140, the surface on a light output surface 135 side of the light guide plate 125 includes a three-sided prism line extending approximately in parallel to the first and second light input surfaces 131 and 133, and the surface on the display panel 120 side includes a cylindrical prism line extending approximately in parallel to the first and second light input surfaces 131 and 133. With this structure, the two-sided prism film 140 functions to convert a direction of light that has entered into the light guide plate 125 from the first light input surface 131 and exited from the light output surface 135 into a direction of the right eye of a viewer, and to convert a direction of light that has entered into the light guide plate 125 from the second light input surface 133 and exited from the light output surface 135 into a direction of the left eye of a viewer.
The display device 110 alternately displays a right-eye image and a left-eye image on the display panel 120, and selectively supplies the right-eye image to the right eye of the viewer and the left-eye image to the left eye of the viewer by illuminating the right-eye image solid-state light source 132 when displaying the right-eye image (and simultaneously turning off the left-eye image solid-state light source 134) and illuminating the left-eye image solid-state light source 134 when displaying the left-eye image (and simultaneously turning off the right-eye image solid-state light source 132). The display device 110 includes a synchronous driving element 150 and an image source 160 in order to enable the above-described operation.
In this kind of backlight 130, when illuminating the right-eye image solid-state light source 132 and when illuminating the left-eye image solid-state light source 134, the uniformity of the brightness in a light guide direction (direction from one of the first and second light input surfaces 131 and 133 to the other) is one important factor for improving the display quality of the display device 110.
Conventionally, a backlight with a barrel-shaped light guide plate 225 like the backlight 200 shown in FIG. 8 has been proposed for the purpose of improving the uniformity of the brightness as described above (for example, refer to Japanese Patent Application Laid-Open No. 2010-198021). In the backlight 200, by curving an bottom surface 236 of the light guide plate 225 into a cylindrical surface shape, the light guide 225 is formed into a barrel shape in which the center portion is thicker than the peripheral portions (at incident end surfaces 231 and 233 at which light sources 232 and 234 are disposed), and a diffusing surface is formed on the bottom surface 236.
Thereby, in the backlight 200, the extraction efficiency from an emitting surface 235 of light that has entered into the light guide plate 225 from one of the light sources 232 and 234 via the corresponding incident end surface 231 or 233 is higher at the other incident end surface 233, 231 side than the incident end surface 231, 233 side through which the light entered, and thus the uniformity of brightness in the light guide direction can be improved.